Piezoelectric device for converting pressure variations into potential variations



Nov. 16, 1948. w H. STIGTER PIEZOELECTRIC DEVICE FOR CONVERTING PRESSURE VARIATIONS INTO POTENTIAL VARIATIONS Filed Jan. 19, 1943 INVENTOR ATTORNEY Patented Nov. 16, 1948 UNITED STATES PATENT OFFICE PIEZOELECTRIC DEVICE FOR. CONVERTING PRESSURE VARIATIONS INTO POTENTIAL VARIATIONS Willem Hendrik Stigter, Eindhoven, Netherlands, assignor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application January 19, 1943, Serial No. 472,919 In the Netherlands August 31,1940

Section 1, Public Law 690, August 8, 1946 Patent expires August 31, 1960 For measuring pressure variations it is known to use piezo-electric members which convert pressure variations into electrical potential variations that can readily be read or registered from a distance. The transmission of the pressure to the said members is generally effected by means 9 Claims. (01. 1'z1--327) of a diaphragm which, either directly or by the V should be exercised on the crystals and that the pressure variations to be measured should be superimposed upon this preliminary pressure.

The invention has for its object to provide such a construction of a pressure indicator that the desired preliminary pressure can be obtained without the sensitiveness to pressure variations being lowered.

According to the invention, this object is achieved by the arrangement of a separate resilient member which receives the preliminary pressure. The diaphragm thus relieved of this pre liminary pressure can be kept thin so that sufflcient sensltiveness is ensured.

In order that the invention may be clearly understood and readily carried into effect it will now be described more fully with reference to the accompanying drawing, in which one form of construction of a pressure indicator according to the invention is shown.

The indicator comprises a metal bushl to the lower end of which a thin diaphragm 2 is secured.

The bush enclose two crystals 3 and 4, a resilient member 5, a head 6, an intermediate plate I with a leading-out wire and an adjusting nut 8. The resilient member 5, which comprises three small dish-springs, bears on a shoulder in the bush 1 and on the other side engages the head 6.

The crystals 3 and 4 with intermediate plate I are clamped, with the interposition of very thin copper plates, between the head 6 and the adjusting nut 8.

By means of this adjusting nut B the spring body can .be compressed to the extent of the required preliminary tension, for example 100 atm., existing on the crystals 3 and 4.

In addition, the dimensions and materials should be such that the preliminary pressure on the crystals becomes substantially independent of the temperature. This is necessary since the crystals, for example when in use, assume a comparatively high temperature (300 C. and over), which may lead to erroneous indications.

What I claim is:

1. A piezo-electric pressure indicator comprising a piezo-electric element, a diaphragm member mechanically connected to the piezo-electrie element for applying a variable pressure thereto, means for applying a preliminary pressure to the piezo-electrlc element, and resilient means interposed between the piezo-electric element and the diaphragm member to relieve the diaphragm member of the preliminary pressure applied to the piezo-electric element.

2. A piezo-electric pressure indicator comprising a housing provided with a bore, a piezo-elec tric element within said bore, a diaphragm member secured to said housing at one end of the bore and mechanically connected to the piezoelectric element, means within said bore for applying a preliminary pressure to the piezo-electric element, and an annular resilient member interposed between the piezo-electric element and the diaphragm member and peripherally supported within said bore to relieve the diaphragm member of the preliminary pressure applied to the piezo-electric element.

The length of the head 6 is chosen to be such that the diaphragm 2 will then bear'on it without any appreciable preliminary tension.

ber secured to said housing at one end of the bore and mechanically connected to the piezoelectric element, means within said bore for applying a preliminary and adjustable pressure to the piezo-electric element comprising a nut member threadingly engaging the bore of the housing and mechanically connected to the piezo-eleotric element, and an annular resilient member interposed between the piezo-electric element and the diaphragm member for relieving the diaphragm member of the preliminary pressure applied to the piezo-electric element, said annular resilient member having a side portion thereof mechanically connected to the piezo-electric element and the peripheral portion thereof supported within said bore.

4. A piezo-electric pressure indicator comprising a housing provided with a bore having a narrow annular shoulder at one end of the bore; a piezo-electric element supported within the bore;

an adjustable fixed pressure head on one side ofthe piezo element; a movable pressure head on the other side of the piezo element; resilient pressure biassing means to exert an initial pres- .sure on the movable pressure head, saidmeans ing a piezo-electric element: means for impressing an initial compression stress on the piezoelectric element, said means consisting of an adjustably movable member presenting a compression surface to the piezo element and a stationary member presenting a reaction surface to the piezo element, means holding the movable member and the stationary member in selected adjusted position; and a pressure-responsive member disposed to engage the piezo element irom the reaction surface side in such manner as to add to the initial compression stress, an external pressure as received by the pressureresponsive member, and that is to be measured by the indicator.

6. A piezo-electric pressure indicator as set forth in claim in which the member that is responsive to the external pressure to be measured consists of a diaphragm peripherally seated and with its center free to move in response to an external pressure and operative to transfer that pressure against the piezo element.

7. A piezo-electric pressure indicator as in claim 5, in which the member that is responsive to the external pressure to be measured consists of a-diaphragm peripherally seated on a part of the holding means spaced farther from the piezo element than the reaction surface; the center of the diaphragm being so mechanically coupled to the piezo element that any external pressure force received by the diaphragm is transmitted to the Number piezo element in addition to the reaction pressure.

8. A piezo-electric pressure indicator as in claim 5, in which the holding means is substantially a hollow-cylinder having one end externally threaded to permit the indicator to be threaded as a plug into a wall of a pressure container; and in which the member to be responsive to the external pressure is a closure element for the inner end of the plug consisting of a diaphragm peripherally sealed in the plug wall with the center of the diaphragmiree to move and normally directly mechanically coupled to the piezo element to transmit to that element any pressure impressed upon the diaphragm.

9. A piezo-electric pressure indicator as in claim 5, including a floating pressure element engaging the reaction pressure side of the piezo element; an annular pressure-biassing element disposed between the floating pressure element and the stationary reaction-surface member, the floating pressure element having a central surface to receive a pressure force other than the force from the annular pressure-biassing element; and in which the member that is to be responsive to the external pressure is supported to just engage the central surface of the floating pressure element, so any external pressure will be transmitted to the floating member in addition to the biassing stress from the pressure-biassing member.

vWILLE'li/I HENDRIK STIGTER.

REFERENCES CITED The following references are of record in the Name Date 1,980,888 Thomas Nov. 13, 1934 2,096,826 Schrader Oct. 26, 1937 2,096,827 Schrader Oct. 26, 1937 2,164,638 Brolze et al July 4, 1939 2,248,574

Knight July 8, 1941 

